The apology came after a meeting with executives from the players union and MLB officials.
"I met today with Major League Baseball and the Players Association and was happy to have the chance to answer questions about my press conference the other day and to learn more about the drug-testing program and on-field disciplinary suspensions," Wells said.
"Now that I have had this opportunity to sit down and discuss the issues, I better understand the procedures that go with steroid testing. I understand that I was wrong in my statements about these issues and for that I apologize."
On Monday, Wells, who had his six-game suspension for making contact with an umpire upheld, verbally bashed Selig about the steroids-related suspension of Baltimore's Rafael Palmeiro.
For the season, the 42-year-old left-hander is 11-6 with an ERA of 4.44.